Re: virtual+static
sunil wrote:
I am dealing with problem where I need virtual+static function:
enum {A=0,B=1};
Factory.cpp:
------------------
Base * createInstance(int classType,char *name)
{
if(classType == A)
{
return dynamic_cast<Base *> ( A::getInstance(name));
There seems to be no need for the dynamic_cast, conversion from
a pointer to the derived to a pointer to the base class is implicit
and provided by the language.
}
else if(classType == B)
{
return dynamic_cast<Base *> (B::getInstance(name));
}
}
base.cpp:
---------------
class Base {
public:
virtual getInstance(string name)=0; //Pure virtual
};
class A:public Base {
public:
static getInstance(string name)
{
if(name already in objList)
return objinlist;
else
return new A();
}
private:
A(){}
List<A> objList;
}
class B:public Base {
public:
static getInstance(string name)
{
if(name already in objList)
return objinlist;
else
return new B();
}
private:
B(){}
List<B> objList;
}
getInstance() is made static in concrete class as we want it to be
able to create instances of that class (hence it has to be static,
since we all this method on class itself)
getInstance() is made pure virtual in base class since I want to
"enforce" the rule that ever yclass deriving from base must implement
this method. If someone doesnt and tries to create a instance, he will
get compile error.
However above code fails to compile:
The function A::getInstance cannot be both virtual and static. This is
a valid case where I need this functionality from design point of
view, but C++ doesnt allow me to do that. Is there any way I can get
around this?
What happens if you drop the 'getInstance' from 'Base' altogether?
V
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